[In most mixed reality apps the boundary is] superfluous, since you can already see the environment around you, and downright annoying because it means you can't utilize your full room as a playspace.

Since v57 of the Meta XR Core SDK select whitelisted developers have been allowed to disable this boundary. Now with v66 of the SDK, any developer can do this.

The only "catch" is that the boundary will only be disabled while passthrough is being rendered, ie. in mixed reality. Fully immersive VR still requires the boundary, which makes sense for safety reasons given you can't see your surroundings.